The present invention relates to a rubber composition comprising a rubber component composed of an ethylenic copolymer rubber and an acrylic rubber and having a good balance among low temperature resistance, oil resistance, heat aging resistance, and strength characteristics.
In recent years, a remarkable technical advance of various industries, such as automobiles, electric appliances, and machinery, made it necessary for rubber materials for use in various related parts to have versatile characteristics. It is known in the art that various special elastomers are being developed in order to meet these requirements.
In particular, in an automobile industry, further advanced performances are required for these elastomers. For example, an elastomer having well-balanced properties in respect of low-temperature flexibility besides heat aging resistance at a high temperature (175.degree. C.) and lubricant oil resistance are desired.
Examples of the elastomer of the kind as described above which has been used in the art include an ethylenic copolymer rubber comprising ethylene-methyl (meth)acrylate and an acrylic rubber.
Although the ethylenic copolymer rubber is excellent in low temperature resistance, heat aging resistance and strength characteristics, it is poor in oil resistance. Accordingly, in order to eliminate this drawback, an attempt has been made to increase the (meth)acrylate content of the ethylenic copolymer rubber comprising ethylene and a (meth)acrylate. However, an increase in the content of the (meth)acrylate brings about a lowering in the molecular weight of the ethylenic copolymer rubber, which makes it impossible to attain not only satisfactory performances as the rubber but also good oil resistance. Therefore, other expedients for improving these properties have been desired.
On the other hand, the acrylic rubber is excellent in the oil resistance and heat aging resistance, but it is poor in the low temperature resistance. In order to solve this problem, studies have been made on rubbers wherein the alkyl group of the (meth)acrylate has been converted into a butyl group or an alkoxy group. However, these rubbers bring about lowerings in both the heat aging resistance and strength characteristics, and no elastomer having a good balance among the low temperature resistance, heat aging resistance, and strength characteristics has been developed.